An image forming apparatus, such as a printer, copier, and the like, and post-processing device thereof are mostly equipped with a paper loading table for temporarily storing plural sheets of paper having images formed thereon within the apparatus and also equipped with a paper discharge tray located outside the apparatus and loaded with the discharged paper. When paper is discharged onto the paper loading table or the paper discharge tray (hereinafter, collectively referred to as a paper loading table), there is a problem in that the paper loading position is deviated during the period after a sheet of paper left the paper conveyance roller (hereinafter, referred to as a discharge roller) located immediately before the paper loading table and before the sheet of paper drops by its own weight onto the paper loading table; consequently, the paper is not loaded on the paper loading table in the aligned state. This problem tends to arise regardless of whether the paper loading table is horizontally disposed or the paper loading table is disposed with the loading surface thereof inclined. Particularly, this problem tends to arise when the paper conveyance speed is high or environmental conditions are severe (high-temperature and high-humidity condition, or low-temperature and low-humidity condition). Furthermore, it is comparatively easy to align a sheet of paper by an alignment device for aligning paper in the direction (paper width direction) perpendicular to the paper conveying direction when the sheet of paper is discharged. However, it is difficult to align the sheet of paper in the paper conveying direction. In order to improve the paper alignment condition in the paper conveying direction on the paper loading table, a variety of paper discharge apparatus have been developed. However, there are problems in that the mechanism is complicated and the device becomes too large, or the sheets of paper are not loaded in the aligned state.
To address the above problems, there is disclosed a technology wherein the rear end of discharged paper is held by a gripper, and the gripper is moved, thereby loading the paper onto the paper discharge tray (for example, see Japanese Patent Application Publication: No. 2008-273656). The technology described in Japanese Patent Application Publication: No. 2008-273656 is also advantageous because the technology can apply to stapled paper and shift-processed paper.